Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE). LTE/LTE-Advanced is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.
A wireless communication network may include a number of base stations that can support communication for a number of mobile devices. In some technologies, mobile devices may be called access terminals, user equipments (UEs), mobile stations, and the like. A mobile device may communicate with a base station via downlink (DL) and uplink (UL) transmissions. The downlink (or forward link) refers to the communication link from the base station to the mobile device, and the uplink (or reverse link) refers to the communication link from the mobile device to the base station. Each base station has a coverage range, which may be referred to as the coverage area of the cell.
In cellular deployments, a macrocell is used to describe a cell serving a wide region such as rural, suburban, and urban areas. Smaller cells may be deployed in homes, small businesses, buildings, or other limited regions. These small cells fall into different classes such as picocells or femtocells. Picocells may be connected to a service provider's network or a macrocell via a direct backhaul. Femtocells are often connected to a service provider's network via broadband connections or other mediums. In 3GPP terms, these cells may be referred to as Home NodeBs (HNB) for UMTS (WCDMA, or High Speed Packet Access (HSPA)) and Home eNodeBs (HeNB) for LTE/LTE-A networks. Some small cells provide restricted access by UEs having an association with the cell. These restricted access cells may be called closed subscriber group (CSG) cells. Cells (e.g., macrocells, picocells, femtocells, etc.) that provide access to UEs associated with one or more provider networks without a specific association between the UE and the cell may be called open access cells.
While small cells typically transmit at lower power than macrocells, signals from a small cell may be received at a UE with relatively high signal strength compared to signals received from a macrocell. For example, where a UE is located near a cell edge for a macrocell but relatively close to a small cell, the small cell signals received at the UE may be as strong as or even stronger than the signals received from the macrocell. In instances where the small is a CSG cell and the UE is not a member of the CSG cell, the UE will not be able to access the network using the CSG cell and may have difficulty finding and decoding the appropriate signals from the macrocell for establishing a communication link with the macrocell, due to interference from the CSG cell signals.